The removal of particulates from gasses has previously been done either by washing with liquids or by filtering with a permeable mechanical medium. Both of these methods require large equipment which is expensive both to install and to maintain.
The use of mechanical filtering is accompanied by additional problems when the gas to be purified is both dirty and hot such as in the case of the exhaust gas effluent of reduction furnaces e.g. carbide furnaces. The exhaust gas may have temperatures of from 800 to 1000.degree. C and contains a great amount of dust. Most filter materials are destroyed at temperatures in this range. In addition, the large quantity of particulates in the exhaust gas requires frequent cleaning operations to be performed.